This invention relates to an improved vehicle crash barrier for decelerating a vehicle that has left a roadway.
Crash barriers are commonly employed alongside roadways to stop a vehicle that has left the roadway in a controlled manner, so as to limit the maximum deceleration to which the occupants of the vehicle are subjected. Additionally, such crash barriers can be struck from the side in a lateral impact, and it is important that the crash barrier have sufficient strength to redirect a laterally impacting vehicle.
A number of prior art approaches have been suggested for such crash barriers employing an axially collapsible frame having compression resistant elements disposed one behind the other in the frame. Young U.S. Pat. No. 3,674,115, assigned to the assignee of the present invention, provides an early example of one such system. This system includes a frame made up of an axially oriented array of segments, each having a diaphragm extending transverse to the axial direction and a pair of side panels positioned to extend rearwardly from the diaphragm. Energy absorbing elements (in this example water filled flexible cylindrical elements) are mounted between the diaphragms. During an axial impact the diaphragms deform the energy absorbing elements, thereby causing water to be accelerated to absorb the kinetic energy of the impacting vehicle. Axially oriented cables are positioned on each side of the diaphragms to maintain the diaphragms in axial alignment during an impact.
Other examples of such crash barriers are shown in Walker U.S. Pat. No. 3,944,187 and Walker U.S. Pat. No. 3,982,734, both assigned to the assignee of this invention. These systems also include a collapsible frame made up of an axially oriented array of diaphragms with side panels mounted to the diaphragms to slide over one another during an axial collapse. The barriers of these patents use a cast or molded body of vermiculite or similar material or alternately loosely associated vermiculite particles to perform the energy absorption function. Obliquely oriented cables are provided between the diaphragms and ground anchors to maintain the diaphragms in axial alignment during a lateral impact.
Gertz U.S. Pat. No. 4,352,484, also assigned to the assignee of the present invention, discloses an improved crash barrier that utilizes an energy absorbing cartridge made up of foam filled hexagonal lattices arranged to shear into one another in response to the compression forces applied to the energy absorbing cartridge by an impacting vehicle.
Stevens U.S. Pat. No. 4,452,431, also assigned to the assignee of the present invention, shows yet another collapsible crash barrier employing diaphragms and side panels generally similar to those described above. This system also uses axially oriented cables to maintain the diaphragms in axial alignment, as well as breakaway cables secured between the front diaphragm and the ground anchor. These breakaway cables are provided with shear pins designed to fail during an axial impact to allow the frame to collapse. The disclosed crash barrier is used with various types of liquid containing and dry energy absorbing elements.
VanSchie U.S. Pat. No. 4,399,980 discloses another similar crash barrier which employs cylindrical tubes oriented axially between adjacent diaphragms. The energy required to deform these tubes during an axial collapse provides a force tending to decelerate the impacting vehicle. Cross-braces are used to stiffen the frame against lateral impacts, and a guide is provided for the front of the frame to prevent the front of the frame from moving laterally when the frame is struck in a glancing impact by an impacting vehicle.
All of these prior art systems are designed to absorb the kinetic energy of the impacting vehicle by compressively deforming an energy absorbing structure. Because of the potential instability of compressive deformation, these systems use structural members to resist side forces that develop from compression loading. Furthermore, all use sliding side panels designed to telescope past one another during an impact. Because such sliding side panels must slide past one another during an axial impact, they have a limited strength in compression. This can be a disadvantage in some applications.
Another prior art system known as the Dragnet System places a net or other restraining structure transversely across a roadway to be blocked. The two ends of the net are connected to respective metal ribbons, and these metal ribbons pass through rollers that bend the ribbons as they pay out through the rollers during a vehicle impact. The energy required to deform these ribbons results in a kinetic energy dissipating force which decelerates the impacting vehicle. The general principle of operation of the metal deforming rollers is shown for example in Jackson U.S. Pat. Nos. 3,211,620 and 3,377,044 as well as Vanzelm U.S. Pat. No. 3,307,832. The Dragnet System utilizes the metal ribbons in tension, but it is not well suited for use alongside a roadway because metal bending systems are positioned on both sides of the roadway, and the net or other obstruction extends completely across the roadway.
Krage U.S. Pat. No. 4,784,515, assigned to the assignee of this invention, describes a collapsible guard rail end terminal that utilizes a wire cable extending through grommets in legs of the end terminal. The side panels of the end terminal are mounted to slide over one another when struck axially. When the end terminal collapses during an impact, the legs may be rotated such that the grommets work the cable and create a frictional force on the cable. However, the magnitude of the resulting retarding forces is highly variable, due to the variable and unpredictable rotational positions of the legs during the collapse.
Thus, a need presently exists for an improved highway crash barrier that provides predictable decelerating forces to an axially impacting vehicle, that is low in cost, that is simple to install, that utilizes a minimum of cross-bracing of the type required in the past to resist lateral impacts, and that efficiently redirects laterally impacting vehicles.